1. Field of the Invention
The present invention relates to a fundus observation device for observing the state of the fundus oculi of an eye, an opthalmologic image processing unit, an opthalmologic image processing program, and an opthalmologic image processing method.
2. Description of the Related Art
As a fundus observation device, conventionally, a fundus camera has been widely used. FIG. 19 shows one example of the appearance of a conventional, general fundus camera. FIG. 20 shows one example of a composition of an optical system internally accommodated in a fundus camera (e.g. JP Patent laid-open No. 2004-350849). Here, “observation” includes at least a case in which produced fundus images are observed (fundus observations with the naked eye may be included).
First, referring to FIG. 19, an explanation is made regarding the appearance of a conventional fundus camera 1000. This fundus camera 1000 is provided with a platform 3 mounted on a base 2 slidably in the front and rear, right and left directions (horizontal direction). On this platform 3, an operation panel 3a and a control lever 4 are installed for an examiner to conduct various operations.
The examiner may move the platform 3 three-dimensionally on the base 2 by operating the control lever 4. On the top of the control lever 4, an operation button 4a is installed, which is pressed down to obtain fundus oculi images.
On the base 2, a post 5 is installed standing upwards. On the post 5, a jaw rest 6 where the jaw of a patient is to be rested and an external fixation lamp 7 as a light source for fixing an eye E are provided.
On the platform 3, a main body part 8 is installed to accommodate various optical systems or control systems of the fundus camera 1000. Furthermore, the control system may be installed inside the base 2 or the platform 3, etc., or in an external device such as a computer, etc. connected to the fundus camera 1000.
On the side of the eye E of the main body part 8 (the left side of the page in FIG. 19), an objective lens part 8a disposed opposite the eye E is installed. Also, on the examiner's side of the main body part 8 (the right side of the page in FIG. 19, an eyepiece part 8b for observing the fundus oculi of the eye E with the naked is installed.
Furthermore, connected to the main body part 8 is a still camera 9 for producing a still image of a fundus oculi of the eye E and an imaging device 10 such as a TV camera, etc. for producing still images or moving images of a fundus oculi. The still camera 9 and the imaging device 10 are formed removably with respect to the main body part 8.
As a still camera 9, in accordance with various conditions such as the purpose of an examination or the saving method of produced images, etc., a digital camera equipped with imaging elements such as CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor), a film camera, and an instant camera, etc. may interchangeably be used when it is appropriate. The main body part 8 is equipped with a mounting part 8c for interchangeably mounting such a still camera 9.
If the still camera 9 or the imaging device 10 is for taking digital images, the image data of the produced fundus image may be sent to a device such as a computer, etc. connected to the fundus camera 1000 and be observed as a fundus image by being displayed on the display. Also, the image data can be sent to an image storing device connected to the fundus camera 1000 to compile a database and be used as electronic data for creating electronic medical charts, etc.
Furthermore, on the examiner's side of the main body part 8, a touch panel monitor 11 is installed. On this touch panel monitor 11, fundus images of the eye E created based on the video signals output from the still camera 9 (of digital type) or the imaging device 10 are displayed. Moreover, on the touch panel monitor 11, the two-dimensional coordinate system with the center of the screen as the origin is displayed overlapped with a fundus image. When the screen is touched by the examiner at a desired position, the coordinate value corresponding to the touched position is displayed.
Next, referring to FIG. 20, a composition of an optical system of the fundus camera 1000 is described. Before imaging of a fundus oculi Ef of the eye E, the optical system of the fundus camera 1000 is aligned with the fundus oculi Ef (that is, the optical system is placed at a suitable position for imaging by moving the optical system in the x, y, and z directions as shown in FIG. 20). The optical system of the fundus camera 1000 is provided with an illuminating optical system 100 to light the fundus oculi Ef of the eye E, an imaging optical system 120 to guide the fundus reflection light of the illumination light to the eyepiece part 8b, the still camera 9, and the imaging device 10.
The illuminating optical system 100 comprises: an observation light source 101, a condenser lens 102, an imaging light source 103, a condenser lens 104, exciter filters 105 and 106, a ring transparent plate 107, a mirror 108, a liquid crystal display (LCD) 109, an illumination diaphragm 110, a relay lens 111, an aperture mirror 112, and an objective lens 113.
The observation light source 101 consists of a halogen lamp, etc. and emits continuous light for observing the fundus oculi. The condenser lens 102 is an optical element that converges the continuous light (observation illumination light) emitted by the observation light source 101 and substantially evenly irradiates the observation illumination light to the fundus oculi.
The imaging light source 103 consists of a xenon lamp, etc. to be flashed at the time of production of fundus oculi Ef images. The condenser lens 104 is an optical element that converges the flash light (imaging illumination light) emitted by the imaging light source 103 and irradiates the fundus oculi Ef evenly with the imaging illumination light.
The exciter filters 105 and 106 are filters to be used when fluorography of images of the fundus oculi Ef takes a place. The exciter filters 105 and 106 respectively can be inserted to and removed from the optical path by a drive mechanism (not illustrated) such as a solenoid, etc. The exciter filter 105 is disposed on the optical path in the event of FAG (fluorescein angiography). Whereas, the exciter filter 106 is disposed on the optical path in the event of ICG (indocyanine green angiography). Furthermore, when color images are being obtained, both the exciter filters 105 and 106 are retracted from the optical path.
The ring transparent plate 107 is disposed in a conjugating location with a pupil of the eye E, and is equipped with a ring transparent part 107a taking an optical axis of the illuminating optical system 100 as a center. The mirror 108 reflects the illumination light emitted by the observation light source 101 or by the imaging light source 103 in the direction of the optical axis of the imaging optical system 120. The LCD 109 displays a fixation target (not illustrated) for fixing the eye E.
The illumination diaphragm 110 is a diaphragm member to shut out a part of the illumination light for prevention of flare, etc. This illumination diaphragm 110 is composed movably in the light axial direction of the illuminating optical system 100, thereby being capable of changing the illuminating region of the fundus oculi Ef.
The aperture mirror 112 is an optical element to combine an optical axis of the illuminating optical system 100 and an optical axis of the imaging optical system 120. In the center region of the aperture mirror 112, an aperture part 112a is opened. The optical axis of the illuminating optical system 100 and the optical axis of the imaging optical system 120 are to be crossed at a substantially central location of the aperture part 112a. The objective lens 113 is installed in the objective lens part 8a of the main body part 8.
The illuminating optical system 100 having such a composition illuminates the fundus oculi Ef in the following manner. First, during fundus observation, the observation light source 101 is lit, and the observation illumination light is emitted. This observation illumination light irradiates the ring transparent plate 107 through the condenser lenses 102 and 104. (The exciter filters 105 and 106 are retracted from the optical path.) The light passed through the ring transparent part 107a of the ring transparent plate 107 is reflected by the mirror 108, passed though the LCD 109, the illumination diaphragm 110 and the relay lens 111, and reflected by the aperture mirror 112. The observing illumination light reflected by the aperture mirror 112 advances in the optical axial direction of the imaging optical system 120 and is converged by the objective lens 113, thereby entering the eye E and illuminating the fundus oculi Ef.
At this moment, the ring transparent plate 107 is disposed in a conjugating location with the pupil of the eye E, and a ring-shaped image of the observation illumination light entering the eye E is formed on the pupil. The fundus reflection light of the observation illumination light is to be emitted from the eye E through a central dark part of the ring-shaped image on the pupil. Thus, an effect of the observation illumination light entering the eye E on the fundus reflection light of the observation illumination light is prevented.
On the other hand, at the time of imaging of the fundus oculi Ef, flush light is emitted from the imaging light source 103 and the imaging illumination light is irradiated onto the fundus oculi Ef through the same path. In the case of fluorography, either the exciter filter 105 or the exciter filter 106 is disposed selectively on the optical path depending on whether FAG imaging or ICG imaging is carried out.
The imaging optical system 120 comprises: the objective lens 113, the aperture mirror 112 (the aperture part 112a thereof), an imaging diaphragm 121, barrier filters 122 and 123, a variable magnifying lens 124, a relay lens 125, an imaging lens 126, a quick return mirror 127 and an imaging media 9a. Herein, the imaging media 9a is an arbitrary imaging media (image pick-up elements such as CCD, camera film, instant film, etc.) used for the still camera 9.
The fundus reflection light of the illumination light, emitted through the central dark part of the ring-shaped image formed on the pupil from the eye E, enters the imaging diaphragm 121 through the aperture part 112a of the aperture mirror 112. The aperture mirror 112 reflects cornea reflection light of the illumination light, thereby acting so as not to mix the cornea reflection light into the fundus reflection light entering the imaging diaphragm 121. As a result, generation of flare on the observation images and/or produced images is prevented.
The imaging diaphragm 121 is a plate-shaped member at which plural circular light transparent parts of different sizes are formed. The plural light transparent parts constitute different diaphragms with different diaphragm values (F values), and are to be disposed alternatively on the optical path by a drive mechanism (not illustrated).
The barrier filters 122 and 123 can be inserted to and removed from the optical path by a drive mechanism (not illustrated) such as a solenoid, etc. In the event of FAG imaging, the barrier filter 122 is disposed on the optical path. Whereas in the event of ICG imaging, the barrier filter 123 is disposed onto the optical path. Furthermore, at the time of production of color images, both the barrier filters 122 and 123 are to be retracted from the optical path.
The variable magnifying lens 124 is to be movable in the light axial direction of the imaging optical system 120 by a drive mechanism (not illustrated). This makes it possible to change the magnifying ratio in observation and the magnifying ratio in imaging, and to focus images of a fundus oculi. The imaging lens 126 is a lens to focus the fundus reflection light from the eye E on the imaging media 9a. 
The quick return mirror 127 is disposed rotatably around a rotary shaft 127a by a drive mechanism not illustrated herein. At the time of imaging of a fundus oculi Ef with the still camera 9, the fundus reflection light is supposed to be guided to the imaging media 9a by springing up the quick return mirror 127 that is obliquely mounted on the optical path. Whereas, at the time of imaging of a fundus oculi with the imaging device 10 or observation of a fundus oculi with the naked eye of the examiner, the quick return mirror 127 is to be obliquely mounted on the optical path to upwardly reflect the fundus reflection light.
The imaging optical system 120 is further provided, for guiding the fundus reflection light reflected by the quick return mirror 127, with a field lens 128, a switching mirror 129, an eyepiece 130, a relay lens 131, a reflection mirror 132, an imaging lens 133 and an image pick-up element 10a. The image pick-up element 10a is an image pick-up element such as CCD, etc. installed internally in the imaging device 10. On the touch panel monitor 11 a fundus oculi image Ef′ imaged by the image pick-up element 10a is be displayed.
The switching mirror 129 is to be rotatable around a rotary shaft 129a in the same manner as the quick return mirror 127. This switching mirror 129 is obliquely disposed on the optical path during observation with the naked eye and guides the light reflected on the fundus oculi to the eyepiece 130.
Also, when a fundus image is formed by using the imaging device 10, the switching mirror 129 is retracted from the optical path, and the fundus reflection light is guided toward the image pick-up element 10a. In this case, the fundus reflection light is directed toward a relay lens 131, is reflected by the mirror 132, and is focused on the image pick-up element 10a by the imaging lens 133.
The fundus camera 1000 is a fundus observation device to be used for observing the state of the surface of the fundus oculi Ef, that is, the retina. In other words, the fundus camera 1000 is a fundus observation device to obtain a two-dimensional fundus oculi image when the fundus oculi Ef is seen from the corneal direction onto the eye E. On the other hand, in the deep layer of retina, tissues such as the choroidea and sclera exist, and a technology for observing these deep layer tissues has been desired. In recent years, devices for observing these deep layer tissues have been practically implemented (e.g. JP Patent laid-open No. 2003-00543, JP Patent laid-open No. 2005-241464).
The fundus observation devices disclosed in JP Patent laid-open No. 2003-00543 and JP Patent laid-open No. 2005-241464 are devices to which so-called OCT (Optical Coherence Tomography) technology is applied, which are called an optical coherence tomography device. The fundus observation device is a device that, by splitting low coherence light into two to guide one (signal light) of the split lights to the fundus oculi and the other (reference light) to a given reference object, and detecting and analyzing interference light obtained by overlaying the signal light reflected by the fundus oculi and the reference light reflected by the reference object, forms a tomographic image of the surface of the fundus oculi or the deep layer tissue. The optical coherence tomography device is capable of forming a three-dimensional image of the fundus oculi based on plural tomographic images. The optical coherence tomography device disclosed in JP Patent laid-open No. 2003-00543 is generally called a Fourier domain OCT.
The Fourier domain OCT is designed to form a tomographic image having a cross-section in the depth direction (the z-direction in FIG. 20) along a scanning line by scanning and irradiating the fundus oculi with the signal light. Such scanning with the signal light is referred to as B-scan (see NEDO Workshop “Seeing (examining) inside the body from the ‘window’ of the human body, the fundus oculi”—Development of an ultra early diagnostic device for lifestyle-related diseases using the latest optical technologies (held on Apr. 25, 2005), Internet<URL:http://www.nedo.go.jp/informations/koubo/170627—2/besshi 3.pdf>).
In the case of formation of a three-dimensional image, B-scan is performed along a plurality of scanning lines, and an interpolation process is applied to the resulting plurality of tomographic images for the generation of three-dimensional image data. This three-dimensional image data is referred to as volume data, voxel data, etc. as in medical imaging diagnosis devices such as an X-ray CT device, and is image data of a form in which pixel data (data of brightness, contrasting density, color and so on including a luminance value and a RGB value) is assigned to respective voxels arranged three-dimensionally. A three-dimensional image is displayed as a pseudo three-dimensional image seen from a specified viewing angle obtained by rendering volume data.
There has been a problem such that the state of the layer boundary of the fundus oculi (e.g. retina) cannot be visually identified because the image region directly under the fundus oculi vessel (the position in the +z direction shown in FIG. 20) becomes unclear when tomographic images of the fundus oculi are captured with the conventional optical image measuring apparatus.
For example, as shown in FIG. 21, when there is (a tomographic image of) a fundus oculi vessel V in (an image of) a layer L1′ in the tomographic image G′ of the fundus oculi, an image region V′ located directly under the fundus oculi vessel V becomes unclear due to the effect of the fundus oculi vessel V, and there is a case where the state of a boundary g2′ between the layer L1′ and a layer L2′, the state of a boundary g3′ between the layer L2′ and a layer L3′, and the state of the boundary g4′ between the layer L3′ and a layer thereunder (not shown) cannot be ascertained. As a result, the thickness of each of the layers L1′, L2′, L3′, etc., directly under the fundus oculi vessel V cannot be measured. Therefore, the thickness of the layer at such position is recorded as “0”, “immeasurable”, or the like, and there is a problem such that it is impossible to measure the thickness of the layer over the entire region where the image is captured.
When a user searches such image region V′ by visually identifying the tomographic image G′, considerable time and labor is required, and therefore, it may not be practical in use. In addition, it is difficult to automatically extract the image region V′ from within the tomographic image G′ because it is difficult to specify the fundus oculi vessel V by analyzing the tomographic image G′ (although the fundus oculi vessel V is shown for illustrative purpose in FIG. 21, it is generally impossible to clearly specify the actual fundus oculi vessel as in the above manner). Symbol LS in FIG. 21 represents the signal light (described above) illuminated onto the fundus oculi Ef from the optical image measuring apparatus.